Birds are extremely fascinating creatures with their colourful feathers and sing-song calls. Yet, whenever I watch them gracefully gliding through the air it is almost impossible to fathom that they used to be theropod dinosaurs (the same family as the Tyrannosaurus Rex) trampling through huge forests. Now, when walking through forests and fields we no longer hear the roar of hungry dinosaurs, but rather the tweet of a cute swallow. However, many of us have noticed significant changes in amount bird songs compared to the symphonies we heard in our youth. Are we imagining it? Are there fewer birds? Indeed there are.
Many bird species all over the world are currently in sharp decline. In fact, the decline of adult bird populations is especially severe for migratory insectivorous (diet consists primarily of insects) species (1,2). Together insectivorous (mainly) and grassland species make up most of the bird Species At Risk in the Land Between. (Specifically: Acadian Flycatcher, Bank Swallow, Barn Swallow, Bobolink, Canada Warbler, Cerulean Warbler, Chimney Swift, Eastern Meadowlark, Eastern Whip-poor-will, Eastern Wood-pewee, Evening Grosbeak, Common Nighthawk, Black Tern, Golden-winged Warbler, Grasshopper Sparrow pratensis subspecies, Henslow’s Sparrow, Loggerhead Shrike migrans subspecies, Loggerhead Shrike eastern subspecies, Louisiana Waterthrush, and Olive-sided Flycatcher).
Unfortunately, some Species At Risk birds, such as the Land Between’s own migratory insectivore the Bank Swallow, have experienced declines of up to 98% compared to their historical numbers (to learn more about Bank Swallows please click here) (3). When thinking about the causes for these startling declines it’s important to remember that many migratory bird species are actually transcontinental, flying huge distances across several countries when traveling from breeding to overwintering grounds. The bank swallow, for example, breeds in North America (south of the treeline in Canada and into the northern United States) and then migrates down through Central America, ultimately reaching overwintering grounds in South America (4). This transcontinental nature means that numerous countries have an effect on species survivorship because each stop along the migration route must provide birds with the food and shelter needed to complete their journey. Thus, migratory bird conservation must also follow a transcontinental approach to be effective. We each need to do our part!
Okay so, bird populations are declining, but why? Here we will discuss three of the main causes of reductions in bird population: pesticides, habitat loss and climate change.
Pesticides: Numerous studies have shown that there is a connection between agricultural intensity (the higher the amount of inputs like fertilizer or pesticides the higher the agricultural intensity) and bird population decline. Agricultural land attracts many bird species because they are essentially open meadows or grasslands (this type of habitat in its natural form has been greatly reduced due to land use changes and development). Currently expanding subdivisions, expansive lawns, and even golf courses are attracting grassland birds. When grasslands are natural with native species, they provide ideal foraging and nesting habitat for many of the bird species which are currently in decline. However, the land that these birds are using, no longer functions like natural wild systems and often exposes them to many harmful chemicals. These chemicals, in particular pesticides, not only affect the birds, but also serve their desired purpose – killing insects. Most of these pesticides are non-selective and lead to the death of non-target insect species. It is this reduction in insect populations that is theorized to be the main cause of the severe decline of insectivorous (insect eating) birds. The lack of natural nutritious food and the necessity of altering their traditional diet to the consumption of substitute insects (which are often less nutritious) is a major problem (4). Ultimately, anything that reduces insect populations, including spraying properties for mosquito control, has negative effects on bird populations.
Historically, DDT, which was discovered to have large negative impacts on insect and bird populations, was the commonly used pesticide, but today the culprits are neonicotinoids (2,4). Neonicotinoids, although applied in smaller quantities than other pesticides, are significantly more powerful, take longer to decompose than alternatives (they last longer in the environment) and are harmful to non-target animals (4). For example, when analysing the effects of neonicotinoid applications in the United States, Nocera et al. found that from 2008-2014 55% of plots sampled showed a decline in grassland birds and 35% showed a decline in insectivores (4). In addition, when neonicotinoid use was stopped, only a modest increase in birds populations were seen (4). This means that pesticides are having long lasting impacts on ecosystems. Natural insecticides are also wreaking havoc like, for example, those that use pyrethrum. Although natural, these sprays contain nerve tonics that are derived from the chrysanthemum flowers and are applied at much higher concentrations than would be found in nature. This then results in broad spectrum negative impact across many species of insects (including moths and dragonflies) and even mammals. (9)
Habitat loss: As previously mentioned, many birds found in Canada are migratory species which travel between different counties. This means that environmental regulations and industry development in other countries have effects on bird species and populations ultimately found in the Land Between. Thus, changes to breeding, migratory or overwintering habitats (even in different countries) can all impact bird populations. For instance, Canada provides the valuable breeding habitat required for producing strong young birds which are able to make it through migration. Once the breeding season is over, birds must cross the continent to reach their overwintering habitat, (this traveling period is when many populations experience their highest percentage of mortality) (6). After their long journey, many of these birds overwinter in South America where they will spend the majority of their time (6). Therefore, having healthy intact habitats across their entire migration and lifecycle routes is extremely important in maintaining healthy populations of migratory birds. Loss of habitat at any location along these routes will affect the survivorship of the birds. For example, losses of forested overwintering habitat in the Andes has been linked to the decline of Canada Warblers (6). The loss of forest habitat and increased habitat fragmentation here in Ontario has also had negative effects on bird populations, resulting in the reduced reproductive success of even some of our most abundant bird species like the migratory Red-Eyed Vireo. (10)
Climate change: Birds are reliant on temperature for triggering migration and weather for ensuring the presence of reliable food sources. However, climate change is altering seasonal patterns which effects migration triggers and ultimately changes the timing of migration. This change in migration dates can lead to a mismatch between food availability (when insects or seeds are available) and bird arrival. For example, in some areas, birds won’t be present during periods of optimal insect abundance. This mismatch has been shown to have negative consequences on birds during breeding season and on their ability to feed offspring (7). In addition, climate change has affected the geographical ranges of various bird species, with many North American species shifting Northward (8). Thus, some species of birds are less likely to be present in certain parts of their historical ranges.
Our bird populations are facing problems both within and outside the borders of the Land Between; however this does not mean they are beyond our help! Consider creating habitat on your property to support populations of our musical friends! Try planting pollinator gardens full of native species, keeping your shorelands natural, leaving trees (when safe to do so) and installing bird boxes to invite these declining species to enjoy a healthy life on your property! By creating natural and connected spaces you will not only help birds, but will also help support pollinators and other wildlife too!
Written by Fallon Hayes, Communications and Education Specialist
- Rioux Paquette, Sébastien, et al. “Severe recent decrease of adult body mass in a declining insectivorous bird population.” Proceedings of the Royal Society B: Biological Sciences 281.1786 (2014): 20140649.
- Li, Yijia, Ruiqing Miao, and Madhu Khanna. “Neonicotinoids and decline in bird biodiversity in the United States.” Nature Sustainability 3.12 (2020): 1027-1035.
- Nocera, Joseph J., et al. “Historical pesticide applications coincided with an altered diet of aerially foraging insectivorous chimney swifts.” Proceedings of the Royal Society B: Biological Sciences 279.1740 (2012): 3114-3120.
- Wilson, Scott, et al. “Drivers of demographic decline across the annual cycle of a threatened migratory bird.” Scientific Reports 8.1 (2018): 1-11.
- González‐Prieto, Ana M., et al. “Topography of the Andes Mountains shapes the wintering distribution of a migratory bird.” Diversity and Distributions 23.2 (2017): 118-129.
- Both, Christiaan, et al. “Climate change and population declines in a long-distance migratory bird.” Nature 441.7089 (2006): 81-83.
- McClure, Christopher JW, et al. “Climate change and the decline of a once common bird.” Ecology and Evolution 2.2 (2012): 370-378.
- Wolansky, M. J., & Harrill, J. A. (2008). Neurobehavioral toxicology of pyrethroid insecticides in adult animals: a critical review. Neurotoxicology and teratology, 30(2), 55-78.
- Burke, D. M., & Nol, E. (2000). Landscape and fragment size effects on reproductive success of forest‐breeding birds in Ontario. Ecological Applications, 10(6), 1749-1761.